ENVIRONMENTAL PROFILE | CHAPTER 3


Dry Run Creek channel has been straightened, speeding the movement of water through the system.


A cascade of stresses affects the creek: too much stormwater runoff, increases in the amount of water flowing through the stream, and increases in the number of times each year that large amounts of water pass through. The physical and biological effect of more water in the system includes scouring of the streambed and banks (which also removes aquatic life), burial of much of the stream bottom in silt and sand, and volatile water level changes. These conditions are symptoms of increased impervious cover, which also reduces groundwater recharge. Reduced groundwa- ter recharge in turn reduces baseflow—baseflow provides a stable flow of cold wa- ter to a stream during hot, dry periods.


A 2007 estimate of sediment inputs to Dry Run Creek was 2,752 tons/year, primarily from the middle and upper watershed. At the time, nearly half the sediment enter- ing Dry Run Creek (1,300 tons/year) came from construction projects in the middle watershed (Black Hawk SWCD 2009). This has since been remedied by City ordi- nances (2569, 2570, 2595) addressing erosion control on construction sites. Erod- ing streambanks also contribute a large amount of sediment to the stream, affect- ing primarily upper and middle watersheds. The Black Hawk County SWCD study (2009) found that unstable banks existed on 39 percent of streambanks in the up- per watershed, 66 percent in the middle watershed, and 35 percent in the lower wa- tershed. In many urban streams, armoring one area diverts the energy of the flow downstream, causing damage somewhere else. All these process together severely damage stream habitat for aquatic insects and other small life forms at the base of the food chain. Fish have less food available and also poor habitat for spawning, feeding and resting.


In 2009, a Watershed Management Plan was developed for the Dry Run Creek Wa- tershed (Black Hawk SWCD, 2009). After assessing the watershed, this study’s pri- mary tool for managing runoff from the land was to retain the stormwater from all <2-inch storms. This has been remedied in part by the City’s recent post-construc- tion stormwater ordinance (Chapter 27, Article 6 of City Code: Post-Construction Stormwater Control). Retaining runoff can be accomplished by providing opportu- nities for storage, infiltration, evaporation, and evapotranspiration. Runoff retention also addresses stream erosion, sedimentation, and improves habitat for aquatic life. Another stormwater management recommendation from the study was to address fertilizers, pesticides, organic matter, street and parking lot pollution, and heated stormwater runoff. For example, corn-soybean rotation on nearly all cropland in the watershed can lead to an over-abundance of ammonium fertilizer on fields. De- pending on the timing, the highly-soluble nitrogen can move into soil and be car- ried into streams, raising nitrogen levels there. It was estimated that implementing Best Management Practices (BMPs) can reduce sediment loading to Dry Run Creek by 2,576 tons/acre/year and also reduce the excess volume of water entering the stream by 2,976,800 gallons per year. AES also has collected data that suggest im- plementation of appropriate BMPs can reduce excess nutrient levels.


Three tributaries of Dry Run Creek are listed as impaired for biological life (e.g., fish, stream insects) and/or bacteria. In order for Dry Run Creek to meet its intended uses, the IADNR conducted a Total Maximum Daily Load (TMDL) study (IADNR 2010). The


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